This invention relates to a self-locking nut of the anti-reversing type which includes an anti-reversing pin for interference engagement with the threads of a mating bolt, and to a method for fabricating such self-locking nut.
This invention is concerned with self-locking nuts of a type which are suitable for use in the fabrication of structures such as microwave towers and highway structures. In the fabrication of such structures, it is desirable to use nuts and bolts which have a very effective protective coating to minimize deterioration due to rust, corrosion, etc.
A very effective protective coating for steel nuts and bolts is referred to as "hot dip galvanized"; and one characteristic of this protective coating is that the thickness of the coating is not uniform. With that characteristic, many known types of lock nuts may not be used effectively, since where the hot dip coating is particularly thick, the binding may be so severe that the self-locking nut may not be turned.
A form of self-locking nut which has been found effective for use with bolts treated by the hot dip galvanized process, is a nut having an anti-reversing pin which projects generally radially inward from the nut for interference engagement with the threads of the bolt. In the manufacture of such anti-reversing nut, the interference pin projects radially into the thread bore; and in use that pin will be deflected in one direction or the other, about 30.degree. from the radial position for example, to assume an anti-reversing position relative to the direction in which the nut is being turned on the bolt. The tip of this pin is configured to be received partially within the groove of the bolt thread and to bite into the bolt material when urged in a reverse direction. The pin, which is anchored in the nut, is necessarily elastic to maintain the interference engagement with the bolt thread and maintain the anti-reversing force, which enables it to perform its function as a self-locking nut.
When it is desired to remove the nut from the bolt, a high torque must be applied which effects the swinging of the anti-reversing pin in the opposite direction about 30.degree. from the radial position, whereby the nut then becomes anti-reversing in the opposite direction.
To provide an effective self-locking nut for a hot dip galvanized bolt it is desirable that the nut be relatively free spinning for either threading the nut onto the bolt, or for unthreading the nut from the bolt after overcoming the high anti-reversing torque. One reason is to minimize any galling or other defacing of the protective coating on the threads which may result in exposure of the base metal and thereby subject the bolt to rust or other corrosion. Another reason is to facilitate the construction of structures being assembled with nuts and bolts and to promote the safety of the workers who may be laboring at high or otherwise hazardous locations. When working at high locations, such as on microwave towers, the use of power tools is sometimes impractical; and a requirement for applying high torque to these fasteners may be hazardous to the workers who must at all times be concerned with body balance and stability.
Anti-reversing nuts of the type described above which are known in the art include an L-shaped anti-reversing pin having an elongated base leg which is anchored in the nut body in parallel relation to the thread axis, and a shorter transverse leg which is directed radially inwardly for interference engagement with the threads of a mating bolt. In the fabrication of these assemblies, the base leg of the pin is rigidly anchored within the nut body, at its end remote from the interference leg; and the above described deflection of the interference leg about 30.degree. to either side of a radial position for example is allowed principally by the tortional deflection of the free portion of the base leg. The elasticity of the materialy from which this anti-reversing pin is made, then, is quite critical. The pin must have the desired elasticity to maintain the interference tip in engagement with the bolt threads with sufficient force to provide the anti-reversing function. If the pin material is not sufficiently elastic, after one or several deflections of the pin interference arm, the pin may break due to over stressing or may be so weak that it can no longer maintain effective anti-reversing force. If the elasticity of the pin material is too low, the pin may simply not apply sufficient force against the bolt threads to function as an anti-reversing pin.
Having in mind that the interference leg of the anti-reversing pin may deflect about 60 degrees between the anti-reversing position for threading the nut onto to the bolt and the anti-reversing position for unthreading the nut, the elastic requirements are high. It would be desirable to provide a lock nut combination of this type having an interference pin which would apply the desired anti-rotation force against the bolt threads, but wherein the tortional deflection required for the locking pin would be much less than the approximately 60 degrees discussed above.
An object of this invention is to provide an improved self-locking nut of the anti-reversing type, and a method for manufacturing same.
Another object of this invention is to provide an improved self-locking nut of the anti-reversing type which is relatively free spinning while running the nut onto or off from a bolt, and a method for manufacturing same.
A further object of this invention is to provide a self-locking nut of the anti-reversing type which is adapted to be used repeatedly without overstressing, and a method for manufacturing same.
Still another object for this invention is to provide an improved self-locking nut of the anti-reversing type having an anti-reversing pin which projects into interference engagement with the bolt and which is adapted to be oscillated between alternative anti-reversing positions, and a method for manufacturing same.
A still further object of this invention is to provide an improved self-locking nut of the anti-reversing type as set forth in the preceding object, where the entire interference pin is allowed to oscillate in a limited manner, thereby minimizing tortional and bending stresses on the interference pin, and a method for manufacturing same.
Another object of this invention is to provide an improved self-locking nut of the anti-reversing type having an anti-reversing pin which projects into interference engagement with the bolt, wherein the interference end of the pin oscillates through a relatively large angle between opposite anti-reversing positions, and where the opposite end of the pin is mounted to oscillate through a lesser angle to reduce stress failure of the anti-reversing pin.
These objects are accomplished in a self-locking nut which includes an annular body having internal threads, the body having a small bore at one side parallel to its axis. An L-shaped anti-reversing pin has one leg disposed within that small bore, and has its other leg extending toward the thread axis for interference engagement with a mating bolt. One leg of the pin has a latching recess disposed adjacent to its free end and facing away from the other leg, with that latching recess being engaged by displaced metal of the nut body which is flowed into the small bore and recess to retain the pin within that bore. In the improved self-locking nut, the latching recess includes two abuttment surfaces which are disposed in planes parallel to the longitudinal axis of the one leg and inclined at respective acute angles from a plane which is parallel to that longitudinal axis and perpendicular to the plane defined by the two legs of the pin. The displaced metal of the body is disposed to limit oscillation of the free end of the pin within the small bore through the alternating abuttment of the abuttment surfaces with the displaced metal, this limited oscillation allowing the swinging of the other arm of the locking pin between alternative anti-reversing positions with resultant reduced stress on the locking pin.
These objects are also accomplished in a method for fabricating a self-locking nut which includes the following steps. An annular nut body is formed having a threaded bore and a small bore at one side parallel to the thread axis. An L-shaped anti-reversing pin is formed from an elongated shaft of an elastic material. A latching recess is formed in one leg of that pin, adjacent to its free end and facing away from the other leg. The latching recess is formed to include two abuttment surfaces disposed in planes parallel to the longitudinal axis of the one leg, the abuttment surface planes each being inclined at an acute angle to a plane parallel to the longitudinal axis and perpendicular to the plane defined by both legs of the pin. The anti-reversing pin is mounted on the nut body with its one leg confined within the small bore, and with its other leg extending into the threaded bore to interfere with the threads of a mating bolt. Metal of the nut body is flowed or otherwise displaced into the small bore and into the latching recess to latch the pin within that bore, and also in position to be abutted alternately by the two abuttment surfaces whereby the free end of the one leg is oscillatable within that bore between limits determined by the engagement of the abuttment surfaces with the displaced metal. This oscillation of the free end of the locking pin enables the other arm of the pin to swing from one anti-reversing position to another with reduced elastic stress on the pin.